JAMB Physics Past Questions & Answers - Page 411

2,051.

The current in a reverse-biased junction is due to?

A.

minority carriers

B.

electrons

C.

majority carriers

D.

holes

Correct answer is A

the current in reverse biased junction diode is due to minority carriers, that is, the negative charges in the p-semi-conductor, and the positive charges in the n-semi-conductor.

2,052.

A transformer is rated 240v. If the primary coil is 4000 turns and the secondary voltage 12v, determine the number of turns in the secondary coil.

A.

200

B.

100

C.

250

D.

150

Correct answer is A

in a transformer, E S/E P = N s/N p
where E s=e.m.f(voltage)of the secondary
E p=e.m.f(voltage)of the primary
N s=no.of turns in the secondary
N p= no. of turns in the primary.
since E s= V s; and E p= V p.
V s/ V p= N s/N p
∴12/240= Ns/4000
Ns =(12x4000)/240
=200

2,053.

the ray which causes gas molecules to glow is known as

A.

cathode ray

B.

anode ray

C.

molecular ray

D.

gamma ray

Correct answer is A

The ray which causes gas molecules to fluoresce or glow is the cathode rays

2,054.

The charge carriers in gasses are

A.

ions only

B.

electrons and ions

C.

electrons and holes

D.

electrons only

Correct answer is B

The electrons and cations of ionized gas act as charge carriers.

2,055.

A silicon material is dopped with an element of a certain group and an n-type semi-conductor is formed. the most likely group of the element is

A.

V

B.

III

C.

I

D.

II

Correct answer is A

Silicon is a tetra valent (4 valent) element, and in order to produce an n type semi-conductor, it has to be dropped with a penta valent (5valent)element, that, that is element in group five (v)